Background:Propionibacterium acnes (P. acnes) is a microaerophilic anaerobic Gram-positive rod responsible for acne vulgaris. Although it is often considered to be a skin contaminant, it may act as a virulent agent in implant-associated infections. Conversely, spontaneous infectious processes have been rarely described.

Case Description:Here, we describe a 43-year-old female with C1-C2 spondylodiscitis attributed to P. acnes infection. Despite long-term antibiotic treatment, computed tomography demonstrated erosion of the C1 and C2 vertebral complex that later warranted a fusion. One year postoperatively, the patient was asymptomatic.

Conclusions:Clinical knowledge of P. acnes virulence in spontaneous cervical spondylodiscitis allows early diagnosis, which is necessary to prevent or reduce complications such as cervical deformity with myelopathy or mediastinitis.

Propionibacterium acnes (P. acnes) is increasingly recognized as a source of musculoskeletal and vertebral infections, particularly associated with the use of spinal instrumentation.[291012] It is a Gram-positive anaerobic rod that is commonly found on the skin (e.g., acne).[111] Despite its low virulence, this pathogen may cause chronic and/or recurrent infections, particularly involving spinal implants.[1215] Here, we present a case involving the spontaneous onset of a C1-C2 spondylodiscitis attributed to P. acnes.

A 43-year-old female had received both local and oral corticosteroid treatment for facial acne 1 month before presenting with neck/pharyngeal pain and progressive dysphagia. Magnetic resonance imaging (MRI) showed a T2-hyperintense signal involving the dens (C2), accompanied by an extensive inflammatory reaction involving the retropharyngeal space [Figure 1a]. Computed tomography (CT) scan also documented early dens erosion [Figure 1b and c]. Although blood cultures were negative, the C-reactive protein (CRP) level was elevated (29.3 mg/dl), and erythrocyte sedimentation rate (ESR) was 120 mm/h. The patient was afebrile on steroids, but was not on any antibiotics.

Biopsy and culture of the C2 lesion

A biopsy was performed of the C1-C2 level through the posterior oral pharynx. Although the histological finding was consistent with inflammation, cultures remained negative (e.g., for common aerobic and anaerobic pathogens). Ten days later, however, the cultures grew P. acnes, sensitive to linezolid. A second confirmatory biopsy confirmed this diagnosis.

Treatment

The patient was treated for 20 days with linezolid 600 mg, and was placed in a Halo-vest for atlantoaxial instability. Three months later, although laboratory tests documented resolution of the infection, both the MRI [ Figure 2a ] and CT scans [Figure 2b and c ] confirmed marked erosion of left C1-C2 joint/dens that required a transarticular C1-C2 posterior arthrodesis (Magerl's technique in combination with Gallie fixation with heterologous bone graft, Organizzazione Toscana Trapianti OTT). Three and 6 months later, the CT scan showed fusion [ Figure 3 ], the patient was clinically improved, and both CRP and ESR laboratory studies were normal.

Figure 2

(a) Sagittal T2-weighted MR image (STIR) performed at the end of antibiotic therapy showing a reduction of the inflammatory process but initial ongoing of deformity of the dens. Sagittal (b) and coronal (c) CT scan showing pronounced increasing of the erosion of the dens of C2

Figure 3

Several conditions such as diabetes mellitus, immunosuppressive states, intravascular devices, and instrumentation/foreign body implants may result in spontaneous spondylodiscitis.[78] P. acnes is a commensal Gram-positive rod found on the skin, and therefore, is typically considered a local contaminant rather than a pathogen when spondylodiscitis is encountered.[11] Here, however, the patient had acne on the chin that seeded the C1/C2 vertebral complex resulting in vertebral abscess/osteomyelitis with retropharyngeal extension, ultimately warranting posterior cervical fusion despite 3 months of antibiotic therapy (e.g. C1-C2 arthrodesis).

Other cases of cervical spine infections attributed to P. acnes [Table 1] were identified in the literature. Harris et al. reported the primary role of P. acnes in spondylodiscitis after lumbar discectomy performed without fusion.[5] Mhaidli and Hahn highlighted the role of P. acnes as a primary virulent agent in delayed infections typically following secondary spinal fusions.[310] Only six cases of nonsurgery-related primary cervical spine infection caused by P. acnes have been reported.[61314] Harifi described one case of spontaneous cervical C1-C2 spondylitis/osteomyelitis attributed to acne (e.g., SAPHO syndrome; synovitis, acne, pustolosis on the skin, hyperostosis, osteitis).[4]

Table 1

Summary of cervical spine infections attributed to P. acnes unrelated to previous surgery collected from the literature including present case

P. acnes may contribute to spontaneous cervical spondylitis in patients with skin lesions. In this and similar cases, a longer incubation period for microbiological cultures is required if P. acnes is suspected as the cause of infection. Early diagnosis is critical to allow for initiation of appropriate antibiotic therapy for preventing subsequent life-threatening complications.